The present invention relates generally to screw presses, and more particularly, to a screw press of the type wherein a ram is mounted for movement up and down within a press body by way of a spindle having a flywheel mounted thereon, the flywheel being driven by friction disks in alternating directions of rotation through friction gear units associated with the disks.
In order to improve the drive mechanisms for friction gears, particularly when used in friction disk screw drive presses, a number of suggestions have been made. In particular, for relatively heavy screw presses having spindle diameters up to 1,000 mm., it was believed until now that the introduction of considerable quantities of energy within only seconds could be handled only hydraulically or by direct electric drive mechanisms. In such cases, up to six electric or hydraulic motors are grouped around the central disk of the screw press, the motors acting by way of pinions on teeth associated with the central disk. These pinions cannot be disengaged as the press strikes, so that the backlash of the press is fully communicated to the pinions, thereby subjecting them to a high degree of wear. Another disadvantage of these known presses is that the drive mechanisms required are extremely expensive and delicate.
In contrast with the direct hydraulic or electric drive mechanisms, a simple friction drive has been employed in a known screw press of the above type because of its simplicity and its ability to transmit great energy in a short time, and is still being used today in smaller presses. Such a friction drive press is disclosed in British Pat. No. 282,590. However, this known screw press has the disadvantage that only one disk can be used at a time to transmit drive energy to the flywheel, and the further disadvantage that due to the unilateral driving arrangement, the spindle is likewise loaded unilaterally. It has, therefore, been attempted to double the supply of energy by applying two opposed side disks rotating in opposite directions relative to each other. However, this attempt has failed up to now because of the difficulty in actuating reverse motion.
It is an object of the present invention to provide a screw press wherein the wear of the spindle is substantially alleviated.
It is another object of the present invention to provide a screw press, wherein relatively high energy is communicated to the flywheel, and hence, to the spindle.
It is also an object of the present invention to provide a screw press, wherein the return travel of the ram is simply achieved.
It is still another object of the present invention to provide a screw press, wherein very exact adjustments, such as setting of the height of the ram, are achieved with relatively simple means.
The problems encountered in the prior screw presses are solved according to the present invention by providing, in the screw press, a number of friction gear units in which each friction disk is mounted singly on a rotatable, axially displaceable shaft, the friction disks being directly drivable by associated drive motors. The shafts for the friction disks are provided with means for urging the friction disks against the flywheel, and with means for displacing the disks away from the flywheel.
Because a friction gear drive arrangement is employed, but with the provision of a friction gear unit consisting of a friction disk and associated gear driving mechanism, the present invention solves the problems discussed above in a particularly simple, and yet very effective manner.
The present invention is not limited to a specific type of friction gear drive, for example, rotary piston combustion engines, hydraulic motors or electric motors may be provided as drive motors.
In one embodiment, the present invention provides an electric motor as a drive unit, the pinion of the motor meshing with a gear rim provided on the friction disk. With this particular relationship between the drive motor and friction disk, a sufficient gear ratio thereby exists depending on the selection of the number of teeth and diameters for the pinion and the gear rim. Instead of this drive arrangement, a belt drive, V-belt drive, chain drive or the like may be provided.
As a consequence of the broad drive principle, including a friction disk gear and a drive motor pinion, the present invention contemplates that the friction disks can be equipped on their sides opposite from the flywheel with a gear secured to the friction disk and in meshed engagement with the pinion of the electric motor, so that the friction disk itself is equipped on its outer circumference with a gear rim meshing with the pinion of the electric motor, or the friction disk can be equipped with an inner sun gear rim of a smaller diameter than that of the friction disk, with which the pinion of the electric motor meshes. This latter arrangement has the additional advantage that, at a selected gear ratio between the pinion and gear rim, the friction disk is not subjected to any limitations in its diameter, so that it can be enlarged radially outwardly as desired.
In a specific embodiment, the means for moving the friction disk to and from the flywheel includes a piston provided at the free end of the friction disk shaft, the piston being axially displaceable in a cylinder provided in the machine body. With such a piston and cylinder arrangement, the displacement of the friction disk shaft can be effected in a simple manner. For example, in accordance with the present invention, the piston and cylinder unit can be pressurized by a pressure medium, in particular, a hydraulic fluid such as hydraulic oil, compressed air or the like and, theoretically, displacement also by means of an ignitable explosive mixture in the cylinder is possible. The piston and cylinder arrangement can be pressured with a pressure medium alternately on both sides to be moved by corresponding control valves.
It has been found especially expedient to provide a reset spring for the generation of the returning force on the side of the piston opposite its working face and between the piston and a portion of the press body. To adjust the reset path of the friction disk and to compensate for disk drive belt wear, a stop screw is provided in the piston cylinder head.
By mounting the friction disk shaft in a sliding or roller bearing to permit axial displacement of the shaft, the present invention provides an especially sturdily constructed screw press, requiring little maintenance.
To enable the transmission of relatively large forces to the flywheel, the present invention contemplates providing at least two friction gear units arranged about the circumference of the flywheel, preferably symmetrically. In special situations, instead of two friction gear units, there may be provided four, six or more friction gear units about the circumference of the flywheel, preferably also symmetrically, in accordance with the present invention. It will be understood that since the friction gear units, which can be produced in modular form, can be provided about the circumference of the flywheel as needed, the present invention makes possible the use of multiple sources of energy.
The present invention also solves, in a very simple manner, a problem not to be overlooked in screw presses. This problem relates to the difficulty of adjusting tools, i.e., the difficulty of precisely effecting the vertical adjustment of the ram. A known solution consists of briefly pressing the friction disks against the flywheel, and then using a brake for stopping. However, since the relative velocity between the disks can reach a value up to 25 meters per second, not only is a great quantity of energy lost, but also the life of the covering on the working face of the flywheel and of the brake is considerably reduced due to such heavy wear.
These disadvantages are avoided by the present invention in that one of the friction gear units arranged at the circumference of the flywheel is drivable at a low speed in both directions of rotation for adjustment of the ram. The present invention, therefore allows the flywheel to absorb only relatively little energy, which is appropriately controllable by the drive motor. Friction losses are avoided as is considerable wear on the faces of the flywheel and friction disk which rub against each other during operation.
The present invention contemplates several different drive arrangements. In particular, the friction gear unit can be driven by a low speed, reversible motor of high gear ratio so that the gear unit is drivable in both directions. The unit can also be driven by two motors, both acting alternately on the same shaft, one of which is designed for secondary use at a high gear ratio relative to that of the main motor. Further, the friction gear unit can be driven by a reversible pole electric motor having a relatively high pole ratio so that a speed jump between 3,000 rpm and 500 rpm, for example, can be obtained.
Yet another contemplated drive arrangement includes a drive motor with a change gear system to enable the direction of rotation of the disk to be changed.
It may also be provided, according to the present invention, that reversible motors for reversing the direction of the friction disk include motor brakes to enable the ram to be precisely adjusted.
These and other objects, features and advantages of the present invention will become more apparent when read in conjunction with the accompanying drawings.